Automotive auxiliary ladar sensor

ABSTRACT

A vehicle and ladar sensor assembly system is proposed which makes use of forward mounted long range ladar sensors and short range ladar sensors mounted in auxiliary lamps to identify obstacles and to identify potential collisions with the vehicle. A low cost assembly is developed which can be easily mounted within a body panel cutout of a vehicle, and which connects to the vehicle electrical and computer systems through the vehicle wiring harness. The vehicle has a digital processor which interprets 3D data received from the ladar sensor assembly, and which is in control of the vehicle subsystems for steering, braking, acceleration, and suspension. The digital processor onboard the vehicle makes use of the 3D data and the vehicle control subsystems to avoid collisions and steer a best path.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/901,914 filed on May 24, 2013 entitled AUTOMOTIVE AUXILIARY LADARSENSOR, having a common assignee with the present application, thedisclosure of which is incorporated herein by reference.

BACKGROUND

Field

The embodiments disclosed herein relate generally to 3-D imagegeneration and the identification of objects, tracking of objects, roadhazard avoidance, and collision avoidance in short range automotiveapplications and more particularly to a ladar sensor assembly having alaser transmitter, laser sensor and digital processor integrated in anenvelope inserted into a vehicle body panel.

References to Related Art

The 3-D imaging technology disclosed in Stettner et al, U.S. Pat. Nos.5,446,529, 6,133,989 and 6,414,746 provides with a single pulse oftight, typically pulsed laser light, ail the information of aconventional 2-D picture along with the third dimensional coordinates;it furnishes the 3-D coordinates of everything in its field of view.This use is typically referred to as flash 3-D imaging in analogy withordinary digital 2-D cameras using flash attachments for a selfcontained source of light. As with ordinary 2-D digital cameras, thelight is focused by a lens on the focal plane of the LADAR sensor, whichcontains an array of pixels called a focal plane array (FPA). In thecase of a LADAR sensor these pixels are “smart” and can collect datawhich enables a processor to calculate the round-trip time of flight ofthe laser pulse to reflective features on the object of interest. Eachsmart pixel also collects data associated with the returning laser pulseshape and magnitude. One value of these flash LADAR sensors, as opposedto competing designs in which one or more pixels is scanned over thefield of view, is the elimination of the precision mechanical scanner,which is costly, high maintenance and typically large and heavy. Thepixels in the focal plane of a flash LADAR sensor are automatically,registered due to their permanent positions within the array. Further,by capturing a frame of data as opposed to one or a few pixels with onelaser pulse, the data rate is greatly increased while weight and volumeare reduced. Because each frame of data is captured from the reflectionof a short duration laser pulse, moving objects or surfaces ofstationary objects may be captured from a moving platform withoutblurring or distortion.

The driver and passengers of an automobile are exposed to dangers fromother vehicles and a number of road hazards. In avoiding side impacts,grazing contact, or low speed impacts in the driver blind spots a sensoris needed which can be installed in multiple locations on a vehicle atlow cost.

Many systems have been proposed to meet the challenge of using opticalimaging and video cameras in a vehicle system to create 3-D maps ofscenes and models of solid objects, and to use the 3-D database tonavigate, steer, and avoid collisions with stationary or moving objects.Stereo systems, holographic capture systems, and those which acquireshape from motion, have all been proposed and in some casesdemonstrated, but what is lacking is a system with the capability ofrapidly capturing 3-D images of objects and roadway features in the pathof a moving vehicle, or travelling on an intersecting path, and whichcontrols and adapts the host vehicle so as to avoid collisions and roadhazards, and steer the best path.

It is therefore desirable to provide, a low cost side and/or rear shortrange, or proximity sensor to enable such a collision avoidance systemwith full 360 degree capability.

SUMMARY OF THE INVENTION

The embodiments disclosed herein provide a ladar sensor assembly andvehicle wherein the vehicle has a cutout in a body panel at theperiphery of the vehicle with a shape adapted to receive a matingretention feature on the ladar sensor assembly. The vehicle further hasa digital processor, a wiring harness and a first connector attached ata terminus of said wiring harness. The ladar sensor assembly is mountedto the vehicle and includes an envelope enclosing a ladar sensor, theenvelope having at least one transparent section and also having atleast one retention feature. A second connector is adapted to mate withthe first connector of the wiring harness. The ladar sensor assemblyalso includes receiving optics and a laser transmitter with a modulatedlaser light output and a diffusing optic for illuminating a scene in afield of view of the ladar sensor. A two dimensional array of lightsensitive detectors is positioned at a focal plane of the receivingoptics, each of the light sensitive detectors having an output producingan electrical response signal from a reflected portion of the modulatedlaser light output. A readout integrated circuit with multiple unit cellelectrical circuits is also included, each of the unit cell electricalcircuits having an input connected to one of the light sensitivedetector outputs and each unit cell electrical circuit having anelectrical response signal demodulator. A range measuring circuit isconnected to an output of the electrical response signal demodulator toa reference signal providing a zero range reference for the rangemeasuring circuit. A detector bias circuit is connected to at least onevoltage distribution grid of the array of light sensitive detectors. Thedigital processor is connected to receive an output from the rangemeasuring circuit and a temperature stabilized frequency reference isconnected through the digital processor to provide clocking signals.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical collision threat scenario with a secondvehicle approaching a first vehicle from behind and left, typically ablind spot for the driver of the first vehicle;

FIG. 2 is a diagram of a lateral collision threat wherein a secondvehicle has stopped past the limit line at the stop sign, or may beslowly rolling through the limit line as the first vehicle approaches;

FIG. 3 is a system block diagram showing the individual ladar sensorsand the vehicle electrical systems including interconnect, relatedvehicle subsystems, and vehicle central processors;

FIG. 4 is a block diagram showing internal details of the LADAR systemcontroller of FIG. 3, and the external interconnections with individualladar sensors mounted on the vehicle, as well as the host vehicleelectrical systems;

FIG. 5 is a block diagram of a typical ladar sensor;

FIG. 6 shows the details of the electronic circuits common to each unitcell of the readout integrated circuit;

FIG. 7 is a diagram of a first section of an object of interest in thefar field of the field of view of the ladar sensor, the object having aseries of rectangular subsections roughly corresponding to theprojection of a pixel of the detector array of the ladar sensor;

FIG. 8 is a diagram of a second section of an object of interest in thefar field of the field of view of the ladar sensor, the object having aseries of rectangular subsections roughly corresponding to theprojection of a pixel of the detector array of the ladar sensor;

FIG. 9 is diagram showing the time line of a transmitted illuminatingpulse and the reflected light pulse returned from the first section ofthe object of interest shown in FIG. 7, and the effect on the returnedpulse shape of a slanted flat surface;

FIG. 10 is diagram showing the time line of a transmitted illuminatingpulse and the reflected light pulse returned from the second section ofthe object of interest shown in FIG. 8, and the effect on the returnedpulse shape of a stepped orthogonal surface;

FIG. 11 is a schematic diagram of a unit cell input amplifier structurewhich is capable of amplifying the low level current signal receivedfrom an element of the detector array and having the ability to alsopreserve the pulse shape with sufficient detail to allow for latersub-pixel resolution enhancement from a detailed analysis of thereturned pulse shape;

FIG. 12 is a detailed transistor level schematic diagram of adifferential amplifier useful as the core of a transimpedance amplifierdesigned to boost the low level signal current from an element of thedetector array, and which may also serve as a limiting amplifier withfixed or variable gain;

FIG. 13 is a schematic diagram of a pre-bias and pulse drive circuit fora semiconductor laser which may be used as a pulsed illuminating source;

FIG. 14 is a plan view of a low cost auxiliary ladar sensor assemblyembodying many of the features described herein;

FIG. 15 is a side view of a section along line AA of the devicedescribed in FIG. 14, and showing enhanced details of the features ofthe low cost auxiliary ladar sensor assembly;

FIG. 16 is a plan view of a second embodiment of a low cost auxiliaryladar sensor assembly showing optional features which may be installedin the same basic package as shown in FIG. 14;

FIG. 17 is a side view of a section along line AA of the devicedescribed in FIG. 16, and showing enhanced details of the features ofthe low cost auxiliary ladar sensor assembly;

FIG. 18 is an isometric view of the hybrid assembly of the detectorarray and readout integrated circuit described herein; and,

FIG. 19 is an isometric view of the detail of the indium bump situatedatop each of the readout integrated circuit unit cells.

DETAILED DESCRIPTION

This application contains new subject matter related to previous U.S.Pat. Nos. 5,696,577, 6,133,989, 5,629,524, 6,414,746, 6,362,482,D463,383, and U.S. patent application Ser. No. 10/066,340 filed on Jan.31, 2002 and published as US 2002/0117340 A1, the disclosures of whichare incorporated herein by reference.

The embodiments disclosed herein enable a system for collisionavoidance, object and obstacle recognition and avoidance, and ride andsteering control improvements. The benefits are realized through the useof a 3-D imaging facility, comprising a vehicle mounted ladar systemwith an object detection and recognition capability, a steering,braking, and accelerator control system, and a ride and suspensionmodification system. The vehicle mounted ladar system may comprise anumber of side mounted, rear mounted, or forward looking ladar sensorsconnected to a central ladar system controller which synthesizes theavailable data from each of the independent ladar sensors into acomposite 3D map of the immediate area in a full 360 degree arcsurrounding the vehicle. In a preferred embodiment, conventional 2Dstill images or video sequences may be used to improve the quality of 3Dsolid models and scene maps. The multiple ladar sensors each have anilluminating laser module which may incorporate a semiconductor laserwith a modulated laser light output, or a pulsed solid state laser, anda diffusing optic for illuminating a scene in the field of view of theauxiliary/proximity ladar sensor. Each ladar sensor also comprises areceiver module featuring a two dimensional array of light sensitivedetectors positioned at a focal plane of a light collecting and focusingassembly (Focal Plane Array). The ladar sensor may be incorporated intoa headlight, taillight, or other auxiliary lamp assembly. The ladarsensor may also be part of a backup light, rearview mirror assembly, ormounted behind an opening in a bumper or grill assembly, or may be highmounted on a vehicle door or roof support, or other vehicle position.

In the case of a potential side or rear impact, it is important todetect the possible impact, and to relay imagery of the potentiallycolliding object of interest. Additionally, while backing up, ormaneuvering at low speed in parking lots, near curbs, or pedestriantraffic, it is useful to have the advantages of multiple, low costauxiliary ladar sensors mounted strategically on the periphery of thehost vehicle. It is therefore desirable to provide a system which uses aplurality of low cost and compact auxiliary flash LADAR sensors having ashorter range and wider field of view than the main, forward lookingvehicle LADAR sensors. The auxiliary short range LADAR sensors and main,long range LADAR sensors operate together to generate 3D data describingobjects and obstacles on a closing path with the host vehicle.

The present invention is drawn toward providing a low cost auxiliaryladar sensor designed to be used as a side or rear sensor in a vehiclemounted ladar imaging system. The 3D images derived from the auxiliaryladar sensor may reveal objects in the path of the host vehicle, or onan intersecting path, and a maneuver may be calculated to avoid acollision or to reduce peak forces between vehicles, or to crash assafely as possible. The system may also adapt the suspension of thevehicle so as to maintain traction on an irregular road surface, or toavoid dangerous obstacles in the roadway. Each vehicular ladar imagingsystem typically consists of multiple vehicle mounted ladar sensors,divided into two categories. The first category of vehicular ladarsensor is the long range, or primary sensor, typically mounted in aforward location of the vehicle and oriented in the direction of highspeed travel so as to sweep out the path of the vehicle in the directionof travel. The second category of sensor is a shorter range, orauxiliary sensor, typically mounted on the vehicle as a rear or sidesensor, and oriented so as to cover the driver blind spots at minimum,and optimally, a full 360 degree coverage around the periphery of thevehicle. These auxiliary sensors must be low cost to allow for multipleinstallations on the vehicle, and thus to facilitate safe and controlleddriving in reverse gear, lane changing, and turning, etc. Each ladarsensor may have a system control processor with frequency reference andinertial reference, a system memory, a pulsed laser transmitter,transmit optics, receive optics, an array of light detecting elementspositioned at a focal plane of the receive optics, a detector biasconverter for supplying bias voltage to the light detecting focal planearray, a readout integrated circuit, analog-to-digital convertercircuits for producing digital image data from the analog readout ICoutputs, a data reduction processor for adjusting and correcting theimage data, and an object tracking processor for segregating, isolating,identifying, and tracking features and objects in the corrected imagedatabase. When paired with an intelligent vehicle system controller withvehicle, steering, braking, and suspension controls, substantialreductions in impact events, and less frequent and severe damage to theoccupants and the vehicle is expected. Each pixel in a focal plane array(EPA) of the preferred ladar sensor converts impinging laser light intoan electronic signal whose magnitude is sampled in time and stored inmemory within the pixel. Each pixel also uses a clock to time thesamples being taken in response to the captured reflection of the lasertight from a target surface. The ladar sensor typically incorporates ahybrid assembly of focal plane array and readout integrated circuit, andthe readout IC is arranged as an array of unit cell electrical circuits,and each unit cell is arranged to be in an array of identical spacingand order as the mating focal plane array. The ladar sensor in apreferred embodiment is capable of working in a flash mode as describedabove, or in a multi-pulse mode, or in a pulsed continuous-wave mode asthe situation dictates. The collision avoidance and navigation systemincorporating the ladar sensor has a number of features which enablehill 3D object modeling and tracking, as well as scene enhancementsderived from the merging of 2D and 3D data bases and managing of both 3Dladar sensors and conventional 2D video cameras. Each of the lightsensitive detectors of the FPA has an output producing an electricalresponse signal from a reflected portion of the laser light output. Theelectrical response signals are connected to a readout integratedcircuit (ROW) with a corresponding array of unit cell electricalcircuits. Each of the unit cell electrical circuits has an inputconnected to one of the light sensitive detector outputs, an electricalresponse signal demodulator, and a range measuring circuit connected toan output of the electrical response signal demodulator. The demodulatormay be a voltage sampler and analog shift register for storingsequential samples of the electrical response signals, or it maycomprise a mixer, integrator, or matched filter. The demodulation mayalso take place external to the readout integrated circuit, by a fastdigital processor operating on a sequence of digitized samples from eachpixel. The fast digital processor may employ algorithms which utilizeweighted sums of sequential analog samples, or use fast Fouriertransforms, convolution, integration, differentiation, curve fitting, orother digital processes on the digitized analog samples of theelectrical response. The fast digital processor may also employalgorithms which isolate or segment the roadway from other objects andobjects from each other. Such objects may be automobiles, bicycles,motorcycles, trucks, persons, animals, walls, signs, road obstructionsetc. These algorithms may compute position and orientation, as well asobject velocity. Objects, their orientation, position and velocity maybe transferred to a central computer for further processing and decisionmaking. Each unit cell circuit has the ability to preserve the shape ofthe returned ladar pulse, and to make inferences about the shape of thesurface within a pixel boundary as seen projected at a distance from thefocal plane array, based on the shape of the reflected light pulse. Therange measuring circuit is further connected to a reference signalproviding a zero range reference for the modulated laser light output.The individual ladar sensor may also incorporate a detector bias circuitconnected to a voltage distribution grid of the detector array and atemperature stabilized frequency reference.

FIG. 1 depicts a first embodiment of the collision avoidance systeminstalled on a first vehicle 2 involved in a collision threat scenariowith a second vehicle 4, which is overtaking the first vehicle in theblind spot of the driver of the first vehicle 2. The forward radiationpattern 6 of a long range ladar sensor embedded in a first headlightassembly of first vehicle 2 is shown by dashed lines where it sweeps theroadway ahead of the passenger side of the first vehicle 2, and theright edge of the roadway 8. The forward radiation pattern 10 of a longrange ladar sensor embedded in a second headlight assembly of firstvehicle 2 is shown by dashed lines where it sweeps the roadway ahead ofthe passenger side of the first vehicle 2, and at least part of theadjacent lane of traffic 14. The radiation pattern 12 of an auxiliaryladar sensor embedded in a tamp assembly is shown projecting radiallyfrom the left rear corner of first vehicle 2, and overlapping a part ofsecond vehicle 4. Short range radiation patterns 12 are also shownemanating from auxiliary lamp assemblies at the other three corners offirst vehicle 2. The auxiliary ladar sensor in this scenario providesobject data and scene data to central processing unit aboard vehicle 2.The central processing unit aboard vehicle 2 then acts to avoid agrazing collision with second vehicle 4, by sending commands to thevehicle 2 control systems, in this case applying brakes and steering tothe right of the roadway, allowing second vehicle 2 to pass unimpeded.Alternatively, the central processing unit may simply notify theoperator of the vehicle through a graphical display, audio warning, ortactile signal through a transducer embedded in the steering wheel.

FIG. 2 shows a second collision threat scenario. The situation wherefirst vehicle 2 is approaching an intersection with second vehicle 4stopped at the intersection. In this case, second vehicle 4 appears tohave overshot the stop limit line adjacent to stop sign 16 and hasrolled into the crosswalk 18 (shaded area), and in some cases, may stillbe rolling or sliding forward. This scenario could easily, evolve on arain-slickened or icy roadway, where second vehicle 4 might havedifficulty stopping in time. Second vehicle 4 may alternatively beemerging from a blind alley perpendicular and to the right of theroadway edge 14. A headlight assembly 20 containing a long range ladarsensor is shown on first vehicle 2. Also shown is an auxiliary lampassembly 22 containing a short range ladar sensor typically positionedat the four corners of first vehicle 2. The first vehicle 2 hascollected scene and object data concerning second vehicle 4, and theonboard central processing unit has analyzed the combined data anddetermined an impact is possible. An array of sensor data, includinglong range and short range ladar sensors, video/still cameras, GPS orrelative position references (to be described in greater detailsubsequently), is analyzed by the central processor, and commands aresent to the vehicle 2 control systems, in this case, steering to make anemergency lane change, and braking to reduce the closing speed. It isalso possible that second vehicle 4 by means of a side sensor coulddetect the danger and react defensively as well.

FIG. 3 shows a system block diagram showing the relationship andconnections of the major functional blocks of the vehicle ladar sensorsystem. A ladar system controller 24 communicates with all of the ladarsensors mounted on the vehicle. In a typical installation, two longrange units, LRU 1 and LRU 2 20 connect to ladar system controller 24through a set of bidirectional electrical connections. The electricalconnections may also have an optical waveguide and optical transmittersand receivers to transfer data, control, and status signalsbidirectionally between long range ladar sensors 20 to ladar systemcontroller 24. Ladar system controller 24 also communicates with the 4short range units, SRU 1, SRU 2, SRU3, and SRU4 22, each through a setof bidirectional electrical connections. The electrical connections mayalso have an optical waveguide and optical transmitters and receivers totransfer data, control, and status signals bidirectionally between shortrange ladar sensors 22 and ladar system controller 24. Each of the ladarsystem ladars may include data processors to reduce the processing loadon the central processors 24 and 28; for example, developing the pointcloud and isolating/segmenting objects in the field of view and objectspeed from the point cloud. A number (n) of optional visible light 2Dstill or video cameras 40 also connect to the vehicle collisionprocessor 38 and produce scene data complementary to the 3D datagenerated by the various ladar sensors mounted to the vehicle. The 2Dstill or video cameras 40 may also operate at infrared wavelengths asopposed to visible wavelengths typical in the preferred embodiment. Thefields of view of the 2D still or video cameras 40 are designed tooverlap the fields of view of the ladar sensors (20 and 22) installed onthe vehicle 2. Bidirectional electrical connections also serve totransfer 3D data maps, status, and control signals between ladar systemcontroller 24 and the vehicle electrical systems and central processingunit (CPU) 28. At the core of the vehicle, an electronic brain maycontrol all functioning of the vehicle 2, and typically controls allother subsystems and co-processors. The electronic brain, or centralprocessing unit (CPU 28) is here lumped together with the basicelectrical systems of the vehicle, including battery, headlights, wiringharness, etc. The vehicle suspension system 30 receives control commandsand returns status through bidirectional electrical connections, and iscapable of modifying the ride height, spring rate, and damping rate ofeach of the vehicle wheels independently. An inertial reference 32 alsohas a vertical reference, or gravity sensor as an input to the CPU 28. Aglobal positioning reference 36 may also be connected to the vehicle CPU28. The GPS reference 36 may also have a database of ail available roadsand conditions in the area which may be updated periodically through awireless link. A duplex radio link 34 may also be connected to CPU 28,and communicate with other vehicles 4 in close range and which may beinvolved in a future impact, and may also receive road data, weatherconditions, and other information important to the operations of thevehicle 2 from a central road conditions database. The vehicle 2 mayalso provide updates to the central road conditions database via radiouplink 34, allowing the central road conditions database to be augmentedby any and all vehicles 2 which are equipped with ladar sensors and aradio link 34. A collision processor and airbag control unit 38 connectsbidirectionally to CPU 28 as well, receiving inputs from a number ofaccelerometers, brake sensors, wheel rotational sensors, ladar sensors,etc. ACU 38 makes decisions on the timing and deployment of airbags andother restraints.

FIG. 4 is a block diagram showing additional details of the ladar systemcontroller 24, and the interconnections with the cooperating systems ofvehicle 2. The ladar system controller 24 comprises a sensor interface50, which transmits commands to the short range ladar sensors SRU1-4 22,and to the long range ladar sensors LRU1 and LRU2 20. A fiber cable andwire harness 48 provides the physical media for the transfer of thecommands from the sensor interface 50 to the various ladar sensors. 3Ddata and status signals are returned from the various ladar sensors tosensor interface 50 through fiber cable and wire harness 48. Likewise,command signals are sent to a number (n) of 2D cameras 26, and statusand image data are returned from the 2D cameras via wire harness 48 toladar system controller 24. Each long range sensor unit 20 connectsthrough a set of bidirectional connections which logically include thetransmitters and receivers within each long range sensor unit 20, thephysical media of fiber cable and wire harness 48, and the transmittersand receivers of sensor interface 50. Each short range sensor unit 22connects through a set of bidirectional connections which logicallyinclude the transmitters and receivers within each short range sensorunit 22, the physical media of fiber cable and wire harness 48, and thetransmitters and receivers of sensor interface 50. Sensor interface 50receives digital logic levels from scene processor 52 and controlprocessor 44 and conditions these signals for transmission over fibercable and wire harness 48 to the various ladar sensors installed on thevehicle 2. Sensor interface 50 may provide amplification, leveladjustment, digital-to-analog conversion, and electrical-to-opticalsignal conversion for outbound signals from control processor 44 andscene processor 52 intended for one or more of the various ladar sensorsor 2D cameras installed on the vehicle 2. Conversely, for inboundsignals, sensor interface 50 may provide amplification, level shifting,analog-to-digital conversion, and optical-to-electrical conversion for3D or 2D data and status signals sent from any one of the various ladarsensors or 2D cameras installed on the vehicle 2 and then provides thesereceived and/or converted signals to control processor 44 and sceneprocessor 52 as digital signals. The sensor interface 50, including D/Aand A/D signal converters, may reside completely or in part on a readoutintegrated circuit (64 in FIG. 5). Scene processor 52 combines the 3Dframes received from each of the operational ladar sensors into acomposite 3D map of the entire space directly in front of andsurrounding the vehicle 2 and may also merge the 3D map with 2D imagedata received from a number (n) of 2D still or video cameras 26 toprovide enhanced resolution, color, and contrast. The addition ofconventional 2D still or video cameras 26 provide the system withenhanced capability for object identification. Complete 3D maps of thearea surrounding the vehicle 2 are best enabled when the auxiliary,short range sensors 22 are installed. In a preferred embodiment, the sixladar sensors comprised of 2 long range sensors 20 and 4 short rangesensors 22 provide a full 360° field of view, and a 3D map may besynthesized by scene processor 52 for the entire space surrounding andin front of vehicle 2. Some vehicle installations also include rearfacing long range ladar sensors 20 (not shown) to provide an additionalmargin of safety. Overlapping fields of view between long range sensorsmay allow scene processor 52 to eliminate some shadows in the far fieldpattern, or to gain additional shape data which may allow positiveidentification of an object or obstacle in the path of the vehicle 2.Overlapping fields of view between short range and long range sensorsgive scene processor 52 additional shape information on any feature orobject in the combined field of view, as well as a reduction of shadows,owing to the wider angles swept out by the short range sensors 22.Control processor 44 receives status data from the ladar sensorsindicating laser temperature, transmitted laser pulse power and pulseshape, receiver temperature, background light levels, etc, and makesdecisions about adjustments of global input parameters to the variousladar sensors being controlled. Global settings for detector bias,trigger sensitivity, trigger mode or SULAR (Staring Underwater LaserRadar) mode, filter bandwidth, etc. may be sent from control processor44 to a given ladar sensor which may override the local settingsoriginally set or adjusted by a local control processor residing withina particular ladar sensor. SULAR mode and trigger mode operations aredescribed in detail with respect to FIG. 5. A non-volatile memory 46provides a storage location for the programs which run on controlprocessor 44 and scene processor 52, and may be used to store statusdata and other data useful at start-up of the system. A datacommunications port 42 typically comprises an Ethernet port or GigabitEthernet port, but may be a USB, IEEE1394, Infiniband, or other generalpurpose data port, and is connected so as to provide bidirectionalcommunications between the control processor 44 or the scene processor52 and the vehicle electrical systems and central processors 28 throughconnections 54. Connections 54 may be optical, electrical, or acombination of both, and include any transmitters and receiversnecessary to condition and transmit the data signals in both directions.Data communications port 42 may also be a special purpose communicationsport specific to a vehicle manufacturer. The 3D range data derived fromthe reflections of the modulated laser light allows for an initialobject model to be determined, and for some object identification totake place in a processor of the individual ladar sensors installed onvehicle 2. Refinements of the object model may be made at higher levelsin the system where data from the several sensors may be integrated withthe data from previous frames. This capability of looking at historicaldata as well as current data, allows for some road hazards and collisionthreats to be viewed from a plurality of angles as the vehicle 2 travelsforward, thus eliminating some shadows, while additional shapeinformation is developed from the multiple angles of observation. Havingthis additional object data may allow scene processor 52 to refine theobject models stored in memory 46. A more precise object model may allowscene processor 52 or vehicle CPU 28 to make better progress inidentifying the various objects and features which may pose a collisionthreat to vehicle 2.

FIG. 5 is a block diagram of a ladar sensor which describes both longrange ladar sensors 20 and short range sensors 22 typical of thepreferred embodiment. Adaptations of the pulsed laser transmitter 72,transmit optics 70, receive optics 68, and in some cases, programmablechanges to the sampling circuitry of readout integrated circuit 64 maybe effected to provide range enhancement, wider or narrower field ofview, and reduced size and cost. The first embodiment provides a 128×128or 128×64 detector array 66 of light detecting elements situated on asingle insulating sapphire substrate which is stacked atop a readoutintegrated circuit 64 using a hybrid assembly method. In otherembodiments of the design, M×N focal plane arrays of tight detectingelements with M and N having, values from 2 to 1024 and greater areanticipated. The functional elements depicted in FIG. 5 may first bedescribed with respect to the elements of a typical short range ladarsensor 22. A control processor 74 controls the functions of the majorcomponents of the ladar sensor 22. Control processor 74 connects topulsed laser transmitter 72 through bidirectional electrical connections(with logic, analog to digital (A/D) and digital to analog (D/A)converters 76) which transfer commands from control processor 24 topulsed laser transmitter 72 and return monitoring signals from pulsedlaser transmitter 72 to the control processor 74. The logic, includinganalog to digital (A/D) and digital to analog (D/A) converters 76, mayreside completely or in part on the readout integrated circuit. A lightsensitive diode detector (Flash Detector) 75 is placed at the back facetof the laser so as to intercept a portion of the laser light pulseproduced by the pulsed laser transmitter 72. An optical sample of theoutbound laser pulse taken from the front facet of pulsed lasertransmitter 72 is routed to a corner of the detector array 66 as anautomatic range correction (ARC) signal, typically over a fiber opticcable. The pulsed laser transmitter 72 may be a solid-state laser,monoblock laser, semiconductor laser, fiber laser, or an array ofsemiconductor lasers. It may also employ more than one individual laserto increase the data rate. In a preferred embodiment, pulsed lasertransmitter 72 is an array of vertical cavity surface emitting lasers(VCSELs). In an alternative embodiment, pulsed laser transmitter 72 is adisc shaped solid state laser of erbium doped phosphate glass pumped by976 nanometer semiconductor laser light.

In operation, the control processor 74 initiates a laser illuminatingpulse by sending a logic command or modulation signal to pulsed lasertransmitter 72, which responds by transmitting an intense pulse of laserlight through transmit optics 70. In the case of a solid state laserbased on erbium glass, neodymium-YAG, or other solid-state gain medium,a simple bi-level logic command may start the pump laser diodes emittinginto the gain medium for a period of time which wilt eventually resultin a single flash of the pulsed laser transmitter 72. In the case of asemiconductor laser which is electrically pumped, and may be modulatedinstantaneously by modulation of the current signal injected into thelaser diode, a modulation signal of a more general nature is possible,and may be used with major beneficial effect. The modulation signal maybe a flat-topped square or trapezoidal pulse, or a Gaussian pulse, or asequence of pulses. The modulation signal may also be a sinewave, gatedor pulsed sinewave, chirped sinewave, or a frequency modulated sinewave,or an amplitude modulated sinewave, or a pulse width modulated series ofpulses. The modulation signal is typically stored in on-chip memory 78as a lookup table of digital memory words representative of analogvalues, which lookup table is read out in sequence by control processor74 and converted to analog values by an onboard digital-to-analog (D/A)converter 76, and passed to the pulsed laser transmitter 72 drivercircuit. The combination of a lookup table stored in memory 78 and a DAconverter, along with the necessary logic circuits, clocks, and timers80 resident on control processor 74, together comprise an arbitrarywaveform generator (AWG) circuit block. The AWG circuit block mayalternatively be embedded within a laser driver as a part of pulsedlaser transmitter 72. Transmit optics 70 diffuse the high intensity spotproduced by pulsed laser transmitter 72 substantially uniformly over thedesired field of view to be imaged by the short range ladar sensor 22.An optical sample of the transmitted laser pulse (termed an ARC signal)is also sent to the detector array 66 via optical fiber. A few pixels ina corner of detector array 66 are illuminated with the ARC (AutomaticRange Correction) signal, which establishes a zero time reference forthe timing circuits in the readout integrated circuit (ROIC) 64. Eachunit cell of the readout integrated circuit 64 has an associated timingcircuit which is started counting by an electrical pulse derived fromthe ARC signal. Alternatively, the flash detector 75 signal may be usedas a zero reference in a second timing mode. Though the ARC signalneatly removes some of the variable delays associated with transit timethrough the detector array 66, additional cost and complexity is theresult. Given digital representations of the image frames, the same taskmay be handled in software/firmware by a capable embedded processor suchas data reduction processor 60. When some portion of the transmittedlaser pulse is reflected from a feature in the scene in the field ofview of the short range ladar sensor 22, it may be incident upon receiveoptics 68, typically comprising the tens of an auxiliary lamp assemblyand an array of microlenses atop detector array 66. Alternativeembodiments use enhanced detectors which may not require the use ofmicrolenses. Other alternative embodiments of receive optics 68 employdiffractive arrays to collect and channel the incoming light to thedetector array 66 individual elements. Pulsed laser light reflected froma feature in the scene in the field of view of receive optics 68 iscollected and focused onto an individual detector element of thedetector array 66. This reflected laser tight optical signal is thendetected by the affected detector element and converted into anelectrical current pulse which is then amplified by an associated unitcell electrical circuit of the readout integrated circuit 64, and thetime of flight measured. Thus, the range to each reflective feature inthe scene in the field of view is measurable by the short range ladarsensor 22. The detector array 66 and readout integrated circuit 64 maybe an M×N or N×N sized array. Transmit optics 70 consisting of aspherical lens, cylindrical lens, holographic diffuser, diffractivegrating array, or microlens array, condition the output beam of thepulsed laser transmitter 72 into a proper conical, elliptical, orrectangular shaped beam for illuminating a central section of a scene orobjects in the path of vehicle 2, as illustrated in FIG. 1.

Continuing with FIG. 5, receive optics 68 may be a convex lens,spherical lens, cylindrical lens or diffractive grating array. Receiveoptics 68 collect the light reflected from the scene and focus thecollected light on the detector array 66. In a preferred embodiment,detector array 66 is formed in a thin film of gallium arsenide depositedepitaxially atop an indium phosphide semiconducting substrate.Typically, detector array 66 would have a sa of cathode contacts exposedto the light and a set of anode contacts electrically connected to thesupporting readout integrated circuit 64 through a number of indiumbumps deposited on the detector array 66. The cathode contacts of theindividual detectors of detector array 66 would then be connected to ahigh voltage detector bias grid on the illuminated side of the array.Each anode contact of the detector elements of detector array 66 is thusindependently connected to an input of a unit cell electronic circuit ofreadout integrated circuit 64. This traditional hybrid assembly ofdetector array 66 and readout integrated circuit 64 may still be used,but new technology may reduce inter-element coupling, or crosstalk, andreduce leakage (dark) current and improve efficiency of the individualdetector elements of detector array 66. In a preferred embodiment, theelements of detector array 66 may be formed atop a substantiallymonocrystalline sapphire wafer. Silicon-on-sapphire (SOS) substrateswith a thin layer of substantially monocrystalline silicon grownepitaxially over a are available in the marketplace, and are well knownfor their superior performance characteristics. A detector array 66 ofAPD, PIN, or PN junction detectors may be formed of a sequence of layersof p-type and n-type silicon via epitaxial regrowth on the SOS wafers.Boron and aluminum may be used as dopants for any of the p-type siliconepitaxial layers. Phosphorus, arsenic, and antimony may be used asdopants for any of the n-type epitaxial layers. Sapphire substrates witha thin layer of epitaxially grown monocrystalline gallium nitride arealso available in the marketplace (gallium nitride on sapphire, orGNOS), and are widely known as substrates well suited to the fabricationof high brightness blue LEDs. A detector array 66 of APD, PIN, or RNjunction detectors may be formed of a sequence of layers of p-type andn-type gallium nitride (GaN) or indium gallium nitride (InGaN) viaepitaxial regrowth on the GNOS wafers. Silicon and germanium may be usedas dopants for any of the n-type GaN layers. In some cases, magnesiummay be used as a dopant for of the p-type layers in GaN. In a furtherdevelopment, detector array 66 may be fabricated monolithically directlyatop readout IC 64. Detector array 66 may also be formed in a moreconventional manner from compounds of indium gallium arsenide, indiumaluminum arsenide, silicon carbide, diamond, mercury cadmium telluride,zinc selenide, or other well known semiconductor detector system.Readout integrated circuit 64 comprises a rectangular array of unit cellelectrical circuits, each unit cell with the capability of amplifying alow level photocurrent received from an optoelectronic detector elementof detector array 66, sampling the amplifier output, and detecting thepresence of an electrical pulse in the unit cell amplifier outputassociated with a light pulse reflected from the scene and interceptedby the detector element of detector array 66 connected to the unit cellelectrical input. The detector array 66 may be an array of avalanchephotodiodes, capable of photoelectron amplification, and modulated by anincident light signal at the design wavelength. The detector array 66elements may also be a P-intrinsic-N design or N-intrinsic-P design withthe dominant carrier being holes or electrons respectively; in whichcase the corresponding ROIC 64 would have the polarity of the biasvoltages and amplifier inputs adjusted accordingly. The hybrid assemblyof detector array 66 and readout integrated circuit 64 of the preferredembodiment is shown in FIG. 18; and the assembly is then mounted to asupporting circuit assembly, typically on a FR-4 substrate or ceramicsubstrate 222 (reference FIGS. 15-17). The circuit assembly providessupport circuitry which supplies conditioned power, a reference clocksignal, calibration constants, and selection inputs for the readoutcolumn and row, among other support functions, while receiving andregistering range and intensity outputs from the readout integratedcircuit 64 for the individual elements of the detector array 66, andshown in FIGS. 14-17 and described subsequently as a circuit substrate222 and attached electrical components. Many of these support functionsmay be implemented in Reduced Instruction Set Computer (RISC) processorswhich reside on the same circuit substrate 222. A detector biasconverter circuit 84 applies a time varying detector bias to thedetector array 66 which provides optimum detector bias levels to reducethe hazards of saturation in the near field of view of detector array66, white maximizing the potential for detection of distant objects inthe field of view of detector array 66. The contour of the time varyingdetector bias supplied by detector bias converter 84 is formulated bycontrol processor 74 based on feedback from the data reduction processor60, indicating the reflectivity and distance of objects or points in thescene in the field of view of the detector array 66. Control processor74 also provides several clock and timing signals from a timing core 80to readout integrated circuit 64, data reduction processor 60,analog-to-digital converters 62, object tracking processor 56, and theirassociated memories. Control processor 74 relies on a temperaturestabilized or temperature compensated frequency reference 86 to generatea variety of clocks and timing signals. Temperature stabilized frequencyreference 86 may be a temperature compensated crystal oscillator (TCXO),dielectric resonator oscillator (DRO), or surface acoustic wave device(SAW). Timing core 80 resident on control processor 74 may include ahigh frequency tunable oscillator, programmable prescaler dividers,phase comparators, and error amplifiers.

Continuing with FIG. 5, control processor 74, data reduction processor60, and object tracking processor 56 each have an associated memory forstoring programs, data, constants, and the results of operations andcalculations. These memories, each associated with a companion digitalprocessor, may include ROM, EPROM, or other non-volatile memory such asflash. They may also include a volatile memory such as SRAM or DRAM, andboth volatile and non volatile memory may be integrated into each of therespective processors. A common frame memory 58 serves to hold a numberof frames, each frame being the image resulting from a single laserpulse. Both data reduction processor 60 and object tracking processor 56may perform 3D image processing, to reduce the load on a centralprocessing unit normally associated with ladar system controller 24.There are two modes of data collection, the first being SULAR, or aprogressive scan in depth. Each laser pulse typically results in 20“slices” of data, similar to a CAT scan, and each “slice” may be storedas a single page in the common frame memory 58. With each pixel samplingat a 2 nanosecond interval, the “slices” are each a layer of the imagespace at roughly 1 foot differences in depth. The 20 slices represent aframe of data, and the sampling for a succeeding laser pulse may bestarted at 20 feet further in depth, so that the entire image space upto 1000 feet in range or depth, may be swept out in a succession of 50laser illuminating pulses, each laser pulse response consisting of 20“slices” of data held in a single frame entry. In some cases, the framememory may be large enough to hold all 50 frames of data. The number ofslices stored could be enough to map out any relevant distance, with notrigger mode operation required. The reduction of the data might thentake place in an external computer, as in the case of data taken to mapan underwater surface, or a forest with tree cover, or any staticlandscape, where sophisticated post-processing techniques in softwaremay yield superior accuracy or resolution. A second data acquisitionmode is the TRIGGER mode, where the individual pixels each look for apulse response, and upon a certain pulse threshold criteria being met,the 20 analog samples bracketing the pulse time of arrival are retainedin the pixel analog memories, and a running digital counter is frozenwith a nominal range measurement. The 20 analog samples are output fromeach pixel through the “A” and “B” outputs of readout integrated circuit64, which represent the interleaved row or column values of the 128×128pixel of the present design. The “A” and “B” outputs are analog outputs,and the analog samples presented there are converted to digital valuesby the dual channel analog-to-digital (A/D) converter 62. Interleavingthe outputs means one of the outputs (“A”) reads out the odd numberedtines of the readout IC 64, and the other output (“B”) reads out theeven numbered lines of the readout IC 64. Larger detector arrays 66 mayhave more than two digital outputs. The digital outputs of the A/Dconverters 62 connect to the inputs of the data reduction processor 60.A/D converters 62 may also be integrated into readout integrated circuit64. The digital outputs are typically 10 or 12 bit digitalrepresentations of the uncorrected analog samples measured at each pixelof the readout IC 64, but other representations with greater or fewerbits may be used, depending on the application. The rate of the digitaloutputs depends upon the frame rate and number of pixels in the array.In TRIGGER mode, a great deal of data reduction has already transpired,since the entire range or depth space may be swept out in the timeframeof a single laser pulse, and the data reduction processor 60 would onlyoperate on the 20 analog samples stored in each unit cell in order torefine the nominal range measurement received from each pixel (unitcell) of the array. The data reduction processor 60 refines the nominalrange measurements received from each pixel by curve fitting of theanalog samples to the shape of the outgoing laser illuminating pulse,which is preserved by the reference ARC pulse signal. The rangemeasurements may also be refined by curve fitting to a well knownreference pulse characteristic shape. In TRIGGER acquisition mode, theframe memory 58 only needs to hold a “point cloud” image for eachilluminating laser pulse. The term “point cloud” refers to an imagecreated by the range and intensity of the reflected light pulse asdetected by each pixel of the 128×128 array of the present design. InTRIGGER mode, the data reduction processor serves mostly to refine therange and intensity (R&I) measurements made by each pixel prior topassing the R.&I data to the frame memory 58 over data bus 61, and no“slice” data or analog samples are retained in memory independently ofthe R&I “point cloud” data in this acquisition mode. Frame memory 58provides individual or multiple frames, or full point cloud images, tocontrol processor 74 over data bus 90, and to an optional objecttracking processor 56 over data bus 59 as required.

As shown in FIG. 5, data reduction processor 60 and control processor 74may be of the same type, a reduced instruction set (RISC) digitalprocessor with hardware encoded integer and floating point arithmeticunits. Object tracking processor 56 may also be of the same type as RISCprocessors 60 and 74, but may in some cases be a processor with greatercapability, suitable for highly complex graphical processing. Objecttracking processor 56 may have in addition to hardware encoded integerand floating point arithmetic units, a number of hardware encoded matrixarithmetic functions, including but not limited to; matrix determinant,matrix multiplication, and matrix inversion. In operation, the controlprocessor 74 controls readout integrated circuit 64, A/D converters 62,frame memory 58, data reduction processor 60 and object trackingprocessor 56 through a bidirectional control bus 88 which allows for themaster, control processor 74 to pass commands on a priority basis to thedependent peripheral functions; readout IC 64, A/D converters 62, framememory 58, data reduction processor 60, and object tracking processor56. Bidirectional control bus 88 also serves to return status andprocess parameter data to control processor 74 from readout IC 64, A/Dconverters 62, frame memory 58, data reduction processor 60, and objecttracking processor 56. Data reduction processor 60 refines the nominalrange data and adjusts each pixel intensity data developed from thedigitized analog samples received from A/D converters 62, and outputs afull image frame via unidirectional data bus 61 to frame memory 58,which is a dual port memory having the capacity of holding severalframes to several thousands of frames, depending on the application.Object tracking processor 56 has internal memory with sufficientcapacity to hold multiple frames of image data, allowing for multi-framesynthesis processes, including video compression, single frame ormulti-frame resolution enhancement, statistical processing, and objectidentification and tracking. The outputs of object tracking processor 56are transmitted through unidirectional data bus 92 to a communicationsport 82, which may be resident on control processor 74. All slice data,range and intensity data, control, and communications then pass betweencommunications port 82 and a centralized ladar system controller 24,(FIG. 4) through bidirectional connections 94. Power and groundconnections (not shown) may be supplied through an electromechanicalinterface. Bidirectional connections 94 may be electrical or opticaltransmission lines, and the electromechanical interface may be a DB-25electrical connector, or a hybrid optical and electrical connector, or aspecial automotive connector configured to carry signals bidirectionallyfor the short range ladar sensor 22 as well as electrical connectionsfor an auxiliary lamp assembly which may have the short range ladarsensor 22 embedded therein. Bidirectional connections 94 may be highspeed serial connections such as Ethernet, Universal Serial Bus (USB),or Fibre Channel, or may also be parallel high speed connections such asInfiniband, etc., or may be a combination of high speed serial andparallel connections, without limitation to those listed here.Bidirectional connections 94 also serve to upload information to controlprocessor 74, including program updates for data reduction processor 60,object tracking processor 56, and global position reference data, aswell as application specific control parameters for the remainder of theshort range ladar sensor 22 functional blocks. Inertial and verticalreference 32 (see FIG. 3) also provides data to the short range ladarsensors 22 and long range ladar sensors 20 from the host vehicle 2through the vehicle electrical systems and CPU 28 and the ladar systemcontroller 24 as needed. Likewise, any other data from the host vehicle2 which may be useful to the short range ladar sensor 22 may be providedin the same manner as the inertial and vertical reference data. Inertialand vertical reference data may be utilized in addition to externalposition references by control processor 74, which may pass position andinertial reference data to data reduction processor 60 for adjustment ofrange and intensity data, and to object tracking processor 56 forutilization in multi-frame data synthesis processes. The verticalreference commonly provides for measurement of pitch and roll, and isadapted to readout an elevation angle, and a twist angle (analogous toroll) with respect to a horizontal plane surface normal to the force ofgravity. The short range ladar sensor 2 typically employs asemiconductor laser, which may be modulated in several different ways.The long range ladar sensor 20 typically employs a q-switched solidstate laser, which produces a single output pulse with a Gaussianprofile if properly controlled. The pulse shape of a solid state laserof this type is not easily modulated, and therefore must be dealt with“as is” by the receiver section of a long range ladar sensor 20. Theoperations of a short range ladar sensor 22 of the type which aretypically embedded in an auxiliary lamp assembly such as a taillight,turn signal, or parking light are the same as the operations of the longrange ladar sensor 20 with some exceptions. The long range ladar sensor20 and short range ladar sensor 22 may differ only in the type of laseremployed and the type of laser modulation. The transmit optics 70 andreceive optics 68 may also differ, owing to the different fields of viewfor a long range ladar sensor 20 and a short range ladar sensor 22.Differences in the transmitted laser pulse modulation between the longrange ladar sensor 20 and short range ladar sensor 22 may beaccommodated by the flexible nature of the readout IC 64 sampling modes,and the data reduction processor 60 programmability. The host vehicle 2may have a number of connector receptacles generally available forreceiving mating connector plugs from USB, Ethernet, RJ-45, or otherinterface connection, and which may alternatively be used to attach longrange ladar sensors 20 or short range ladar sensors 22 of the typedescribed herein.

In the preferred embodiments described herein, a number of digitalprocessors have been identified, some associated with the host vehicle(total 2), some associated with the ladar subsystem (total 3), and someassociated with the individual ladar sensors (total 3). The partitioningand the naming of these various digital processors has been made basedon engineering judgment, but other partitioning and naming conventionsmay be used without changing the scope or intent, or affecting theutility of the invention. The function of those processors associatedwith the vehicle; the vehicle CPU 28, and the collision processor andairbag control unit 38, may be combined in a single digital processorsome future embodiments. A combined vehicle CPU 28 and collisionprocessor and airbag control unit 38 may also incorporate ladar systemcontroller 24, which is normally associated with the ladar subsystem.The ladar system controller 24 (including scene processor 52 and controlprocessor 44) may in some alternative embodiments be eliminated as acircuit, and only the functions normally performed by ladar systemcontroller 24, as described herein as contemplated for use with thepresent invention, would then be assumed by a more powerful vehicle CPU28. Likewise, the object tracking processor 56 of the individual ladarsensor could be absorbed into the vehicle CPU 28, as could other ladarsensor processors such as data reduction processor 60 and controlprocessor 74. This would follow a trend toward greater centralization ofthe computing power in the vehicle. A trend towards decentralization mayalso take place in reverse, some alternative embodiments having evermore of the processing power pushed down into the ladar sensorsubsystem. In other alternative embodiments, perhaps in a roboticvehicle where only a single ladar sensor might be installed,substantially all of the processing power could be incorporated in theindividual ladar sensor itself. The term digital processor may be usedgenerically to describe either controllers or digital computers, as manycontrollers may also perform pure mathematical computations, or performdata reduction, and since many digital computers may also performcontrol operations. Whether a digital processor is termed a controlleror a computer is a descriptive distinction, and not meant to limit theapplication or function of either device.

Continuing with FIG. 5, the use of a semiconducting laser in a preferredembodiment for a short range ladar sensor 22 allows for tailoring of thedrive current to a Vertical-Cavity Surface-Emitting Laser (VCSEL), oneexample of a semiconductor laser, or any diode laser, so as to produce aGaussian optical pulse shape with only slight deviations. The VCSELresponse time is in the sub-nanosecond regime, and the typical pulsewidth might be 5-100 nanoseconds at the half power points. In thediagram of FIG. 5, the VCSEL and laser driver would be part of thepulsed laser transmitter 72, and the desired pulse or waveshape isitself produced by a digital-to-analog converter 76 which has a typicalconversion rate of 200-300 MHz, so any deviations in the output pulseshape from the Gaussian ideal may be compensated for in the lookup tablein memory 78 associated with control processor 74, which serves as thedigital reference for the drive current waveform supplied to the laserdriver within pulsed laser transmitter 72 by the D/A, converter. AGaussian single pulse modulation scheme works well at short ranges,given the limited optical power available from a VCSEL. Extending therange of a VCSEL transmitter may be done using more sophisticatedmodulation schemes such as multi-pulse sequences, sinewave bursts, etc.The VCSEL, and modulation schemes as described herein with reference toshort range ladar sensor 22 are an alternative to the solid state lasertypically used in a pulsed laser transmitter 72 of a long range ladarsensor 20. The use of a VCSEL array in pulsed laser transmitter 72 hasthe potential to reduce cost, size, power consumption, and/or enhancereliability. Ladar sensors may be mounted at many points on the vehicle2; door panels, rear view mirrors, bumpers, etc. When equipped with amore sensitive detector array 66 such as an image tube FPA, an auxiliaryladar sensor of the type described herein may use a VCSEL array as anilluminating source, and longer ranges may be supported.

The unit cell electronics depicted in FIG. 6 is well adapted to workwith a Gaussian single pulse modulation scheme, and works advantageouslywith other modulation schemes as well, including sequences offlat-topped pulses, Gaussian, or otherwise shaped pulses. These pulsesmay be of varying width and spacing, in order to reduce rangeambiguities, and may also be random pulse sequences, or in other cases,Barker coded pulse sequences. In the typical operation of a short rangeladar sensor 22 having a semiconductor laser producing a single Gaussianoutput pulse, some portion of the pulsed laser light reflected from asurface in the field of view of the short range ladar sensor 22 isconcentrated and focused by receive optics 68 and falls on an individualdetector element 97 of detector array 66. The individual element 97 istypically an avalanche photodiode, but may be a PIN or NIP, or otherstructure. Each individual element 97 of detector array 66 is formed ina semiconducting film comprised of silicon, indium gallium arsenidephosphide, aluminum gallium arsenide, indium gallium nitride, or othersemiconducting compound appropriate to the wavelength of operation. Eachindividual element 97 is biased with a voltage by a bias voltagedistribution network V_(DET) 99. The reflected light signal incidentupon the individual detector element 97 is converted to an electronicsignal, typically a photocurrent, and amplified by input amplifier 96,typically transimpedance amplifier. The output of input amplifier 96 isdistributed to a trigger circuit 98 as welt as a number of analogsampling gates 108. The trigger circuit 98 is typically a thresholdvoltage comparator, set to trigger when a pulse is received whichexceeds a predetermined magnitude, though other pulse detection schemesmay be used. After a programmable delay through delay circuit 100, thestate of circular selector 104 is frozen by the logic transition oftrigger circuit 98 output. Prior to the detection of a received pulse bytrigger circuit 98, the sample clock 102 causes the state of circularselector 104 to advance, enabling one of the sampling control outputsS1-S3, which in turn causes a sampling of the input amplifier 96 outputby one of the sampling gates 108. The number of transitions of sampleclock 102 are counted by counter 106, as the circular selector 104outputs a logic transition to counter 106 for every cycle of thesampling clock after the release of the active low reset line 107.Circular selector 106 may cycle through outputs S1-S3 in order, or mayhave a different order, depending on the programming. A second circularselector 106, and sample clock 102 may operate in parallel, along withcounter 106, analog sampling gates 108 and analog memory cells 110. Thecombination of sample clock 102, counter 106, circular selector 104,sampling gates 108, and memory cells 110 may be termed a unit cellsampling structure 111, indicated by the short dashed line border. Two,three, or more of these sampling structures may be operated in parallelon the output of input amplifier 96, with the advantages of such astructure to be described later in regards to range ambiguity. Shown inFIG. 6 are three sampling gates, and analog memory cells, but the numbermay be several hundred or more on some readout ICs 64. Once all of theanalog sample data has been taken, a control command from the controlprocessor 74 initiates a readout cycle by activating output control 114and output amplifier 112 to readout the contents of the analog memorycells 110 in a predetermined order.

Ia typical short range ladar sensor 22, and assuming a 1 cm² VCSEL arraywith a 5 kW/cm² power density, and depending upon the reflectivity ofthe objects in the field of view, and the responsivity and excess noiseof the detector array 66, the effective range of a Gaussian single pulsemodulation scheme might be in the range of 10-20 meters, using a simplethreshold detection technique. Without resorting to a large VCSEL array,which might be expensive and might require a large discharge capacitorto supply a large current pulse, more sophisticated modulation anddetection techniques can be used to create additional processing gains,to effectively increase the signal-to-noise ratio, and thus extend therange of the short range ladar sensor 22 without requiring an increasein peak power. In a first modulation scheme, which produces a Gaussiansingle pulse modulation, a detection technique may be employed whichuses the digitized analog samples from each unit cell electricalcircuit, and processes these samples in a digital matched filter to findthe centroid of the received pulse, resulting in significant processinggain. The processing gains resulting from this structure areproportional to the square root of the number of samples used in thefiltering algorithm. For example, a unit cell electrical circuit with256 analog memory cells 110 could yield a processing gain of 16 if allthe available analog samples were used in a matched filter algorithm,assuming Gaussian single pulse modulation, and a normal noisedistribution. The term “processing gain” is used here to describe theincrease in effective signal-to-noise ratio (SNR) realized by performingthe described operations on the voltage samples. Assuming the pulsedlaser light is distributed uniformly over just the field of view of thereceive optics 68, the effective range of the ladar also increases asthe square root of the transmitted power (or SNR), and an increase inrange to 40-80 meters could be the result. Single pulse Gaussianmodulation may be characteristic of either a solid state laser or asemiconductor laser with a simple driver, and thus may be an attributeof either a tong range ladar sensor 20 or a short range ladar sensor 22.

The unit cell electronic circuit of FIG. 5 is well adapted to singlepulse modulation, or to more complex modulation scenarios. In a secondmodulation scheme, a VCSEL array modulated with a series of Barkerencoded flat-topped or Gaussian pulses can be sampled by the unit cellelectronics of FIG. 5 and analyzed by data reduction processor 60 forrange and intensity estimates. In a third modulation scheme, a VCSELarray modulated with a pulsed sinewave allows for greater cumulativeenergy to be reflected from a feature in a scene in the field of view ofeither a short range ladar sensor 22 or a long range ladar sensor 20without an increase in peak power. Each peak of a pulsed sinewave willhave a separate reflection from an object or feature in the scene in thefield of view of the ladar sensor (20, 22) and the unit cell electricalcircuit of FIG. 5 allows the ladar sensor receiver to respond to thecumulative energy from many of these reflected pulses using a minimum ofcircuitry. The waveform in a preferred embodiment is a number ofsinewave cycles, and the number could be quite large, depending on anumber of factors. The receiver circuitry of the unit cell electronicsshown in FIG. 5 is capable of sampling or of synchronously detecting thecumulative energy of the returned pulse peaks. Two sampling modes may besupported by the unit cell sampling structure shown in FIG. 5. Whentaking analog samples of single pulse or multi pulse sequences, whereinanalog samples of an incoming waveform are being sequentially taken, thesampling impedance control 109 (Z) to the circular selector 104 would beset to a minimum value. The sampling frequency of sample clock 102 wouldalso be selected to produce 10 or perhaps 20, analog samples during eachpulse width. When the sampling impedance control 109 is set to aminimum, the sample controls S1, S2, S3 . . . turn on with full voltageduring a sampling cycle. Since each sampling gate 108 is a field effecttransistor, increasing the sample control voltage S1-S3 will increasethe gate-source voltage on the sampling FET, thus lowering the impedanceof the channel between source and drain, and setting the sampling gateimpedance to a minimum. When the sampling gate 108 impedance is set to aminimum, the storage capacitor serving as analog memory cell 110 chargesrapidly to the voltage present at the output of input amplifier 96. Thismode can be termed “instantaneous voltage sampling” to distinguish themode from a second sampling mode, which is selected when the samplingimpedance control 109 is set to a higher, or even maximum value. Whenthe sampling impedance control 109 is selected for high impedance, ormaximum series resistance value, the outputs S1-S3 would be at or nearminimum voltages when enabled, resulting in a lower gate-source voltageacross each of the sampling gate FETs 108, and thus a higher samplinggate series resistance in the channel between source and drain of eachsampling gate 108 FET. With the series resistance of the sampling gates108 set to high or maximum value, the effect is to cause an R-C filterto develop, with the analog memory cell 110 storage capacitor performingas an integrating capacitor. This second sampling mode may be veryuseful when a sinusoidal modulation is applied to the pulsed lasertransmitter 72 in the case where the laser is a semiconductor laser,typically a high efficiency VCSEL. By applying a sampling clock to thesampling gate 108 driven by S1, and which is the same frequency as thesinusoidal modulation, a sum frequency and a difference frequency willbe in the sampled signal, and the analog memory cell 110 storagecapacitor will filter out the sum frequency, and the differencefrequency will be zero, leaving only a DC voltage component, which willbe a trigonometric function of the phase difference. Over a number ofcycles of the sinusoidal modulation from the output of input amplifier96, this DC voltage will emerge as the sine or cosine of the phasedifference between the transmitted and received waveforms. This phasedifference is proportional to the range to a reflecting surface. Toimprove the processing gain, the second sampling gate driven by the S2signal is driven by the same sampling clock frequency, but shifted by 90degrees in phase, and the greater of the two DC voltages, or a ratio ofthe two voltages, may used to estimate phase, and thereby range.Typically, a ratio is preferred, as it removes the variation inamplitude of the incoming sinewave as an error term. This type ofdetection relies on “In-phase” and “Quadrature-phase” local references,and is often referred to as an “I&Q” detection scheme. Thus, thesampling gates 108 can be operated as instantaneous voltage samplers ina first sampling mode, or as frequency mixers in a second sampling mode,depending on the state of the sampling impedance control 109, and thefrequency applied by sampling clock 102. In the first sampling mode, theshape of a pulse or sequence of pulses may be acquired, and in secondsampling mode, a periodic waveform modulation such as a sinewave, may bedemodulated through the frequency mixing effect and integration on astorage capacitor, resulting in a phase measurement and thereby range.In a third modulation case, two and perhaps three sinewaves of differentfrequencies are superimposed as a modulation signal on a semiconductorlaser, and the received waveform output from input amplifier 96 issampled by 2 or 3 unit cell sampling structures 111 arranged inparallel, and operating at the 2 or 3 different frequencies of themodulation signal. Each frequency is demodulated and the phase measuredb the unit cell sampling structure tuned to the frequency of interest byfeeding the appropriate sampling frequency from sample clock 102,typically copy of the modulation frequency.

When measuring the phase of reflected laser energy with respect to atransmitted laser sinewave modulation, certain limits must be observed.If the ladar should have a maximum range capability of 150 meters infree space, the total round trip delay from transmit to receive would bearound 1 microsecond. For the phase measurement to be meaningful, thefrequency of transmission must therefore be less than 1 MHz to avoidspatial (distance) aliasing of targets at the 150 meter limit. In otherwords, the further the target, the lower the frequency of modulationmust be for a single modulation frequency phase measurement to bemeaningful. In a conventional sweep radar, the dwell time on the targetis limited, so return signals beyond the maximum design range often donot appear as aliased, or “ghost” signals at a shorter apparent range.In the ladar of the instant invention, the typical mode is a staringmode, and there is no sweep of the illuminating beam or receivingantenna across the target space. Therefore, in the ladar sensor (20,22)of the present design, responses from targets beyond the designedmaximum range could produce an aliased response (one in which the phaseshift is greater than 2π). A method for resolving these aliased, or“ghost” images is to illuminate the target in a second or thirdtransmission with a slightly different frequency; for example 0.95 MHzversus the 1.0 MHz in a first gated sinewave illuminating pulse. If thetarget image remains at the same apparent range, it is likely a realtarget at a range less than the design maximum range limit. If theapparent range of the target shifts at the second illuminatingfrequency, it is likely the image is an aliased, or “ghost” image from atarget at a distance beyond the design maximum range of the ladar sensor(20, 22). The ladar sensor (20, 22) of the instant invention makes useof a frequency agile transmitter which can rapidly tune from a firsttransmission frequency to a second transmission frequency, and more ifnecessary. In a preferred embodiment, the unit cell sampling structure111 is doubled or tripled, and operated in parallel, and two or threesinewave modulation signals are superimposed on the semiconductor lasertransmitter. When using multiple frequency modulation, the individualfrequencies should not be simple harmonics of each other; i.e., theyshould not be related by fractions of low value integers. The ladarsensor (20, 22) in a preferred embodiment makes use of a semiconductorVCSEL laser, enabling the use of shaped single pulses, shaped multiplepulses, shaped and encoded multiple pulses, gated sinewave, gatedchirped sinewave, and multi-frequency gated sinewave modulation schemes.In alternative embodiments, a low power semiconductor laser may beelectronically modulated, and the resulting modulated optical outputamplified by an optical amplifier. By selecting a modulation regimeappropriate to the particular scene or objects to be imaged, theflexible modulation capabilities of the present design result in aminimum sized pulsed laser illuminating source with maximum performancein range and resolution.

Shown in FIG. 7 is a target object which illustrates a key advantage ofthe pulse shape sampling capability of the unit cell electrical circuitof FIG. 6. The dashed line shows an incident plane wave which isperpendicular to surface 118 of object 116. The individual detectors 97of detector array 66 are typically square. Object 116 is at a distancefrom the ladar sensor (here long range sensor 20) so the reflectionsfrom object 116 exactly subtend a 3×3 zone of pixels within the detectorarray 66. Surface 118 is a 1′×1′ square stacked 3 high in a column, andat a distance from the ladar sensor 20 of 100′. Surface 120 is a 1′×1′square stacked 3 high in a column, but at a distance of 104′ from theladar sensor 20. Between surfaces 118 and 120 is angled plane surface122 which slopes rearward 4′ over a 1′ foot width.

Shown in FIG. 8 is a target object which illustrates in a differentmanner the pulse shape sampling capability of the unit cell electricalcircuit of FIG. 6. The dashed line shows an incident plane wave which isperpendicular to surface 126 of object 124. As noted above, theindividual detectors 97 of detector array 66 are typically square.Object 124 is at a distance from the ladar sensor (long range sensor 20)so the reflections from object 124 exactly subtend a 3×3 zone of pixelswithin the detector array 66. Surface 126 is a 1′×1′ square stacked 3high in a column, and at a distance from the ladar sensor 20 of 100′.Surface 128 is a 0.5′×1′ square stacked 3 high in a column, but at adistance of 101.5625′ from the ladar sensor 20. Surface 130 is a 5′×1′square stacked 3 high in a column, but at a distance of 102.4375′ fromthe ladar sensor 20. Surface 132 is a 1′×1′ square stacked 3 high in acolumn, but at a distance of 104′ from the ladar sensor 20.

FIG. 9 shows the time response of object 116 to a Ins trapezoidal pulse132 having 0.5 ns rise and fall times. After an approximate 200 ns gap,reflected pulse 134 returns to detector pixels 1-3 in the leftmostcolumn of the 3×3 illuminated zone of detector array 66 as described inthe discussion of FIG. 7. Reflected pulse 134 has the same shape as thetransmitted pulse 132, since surface 118 is perpendicular to thedirection of propagation of the transmitted pulse 132. Reflected pulse138 returns to detector pixels 4-6 in the center column of the 3×3 zoneof detector array 66, with a leading edge coincident in time with theleading edge of reflected pulse 134. Since the pulse is 1.5 ns in totalwidth, it takes 3 ns for reflected pulse 138 to build up to a fullvalue. Also, it takes 3 ns for the reflected pulse 138 to return fromthe very last edge of surface 122 where it joins to surface 120.Therefore, a total width of 4 ns is at the maximum value, stretching thetotal width of the pulse 8 ns and the peak level by 3 ns. Reflectedpulse 136 returns to detector pixels 7-9 in the rightmost column of the3×3 zone of detector array 66, with a trailing edge coincident in timewith the trailing edge of reflected pulse 138. The pulse shape samplingcapability of the unit cell electrical circuit described on FIG. 6allows the data reduction processor 60 to make an informed estimate ofthe shape of many sub-pixel features conforming to simple geometry asshown, by analyzing the shape of reflected pulses such as reflectedpulse 138. Scene processor 52 may further refine the estimates of thesesub-pixel features by both the pulse shape and surrounding geometry.

FIG. 10 shows the time response of object 124 to a ins trapezoidal pulse132 having 0.5 ns rise and fall times. After an approximate 200 ns gap,reflected pulse 140 returns to detector pixels 1-3 in the leftmostcolumn of the 3×3 illuminated zone of detector array 66 as described inthe discussion of FIG. 8. Reflected pulse 140 has the same shape as thetransmitted pulse 132, since surface 126 is perpendicular to thedirection of propagation of the transmitted pulse 132. Reflected pulse144 returns to detector pixels 4-6 in the center column of the 3×3 zoneof detector array 66, with a shape clearly showing two distinct andoverlapping trapezoids. The first trapezoidal shape is due to reflectionoff the surface 128, and the second trapezoidal shape a result ofreflected light from the more distant surface 130. The separation of thecenters is 1.75 ns, leaving an overlap of ¼ of the tailing edge of thefirst pulse due to surface 128 with ¼ of the leading edge of the secondpulse due to surface 130. The sum of the two ¼ level overlappingresponses results in a ½ level dip between the two emergent trapezoidalfeatures of response pulse 144. Reflected pulse 142 returns to detectorpixels 7-9 in the rightmost column of the 3×3 zone of detector array 66,with a leading edge 8 ns later than the leading edge of reflected pulse140. Since both surface 128 and 130 are orthogonal to the direction ofthe illuminating pulse, no change in width of the top levels isobserved, and the stairstepped shape may be inferred by the datareduction processor 60 operating in concert with the scene processor 52.

FIG. 11 shows the structure of input amplifier 96 of the unit cellelectrical circuit. A difference amplifier 148 has a programmablevoltage reference (V_(REF1)) connected to a non-inverting (+) input. Theinverting (−) input of difference amplifier 148 is connected to theanode of an APD detector element 97 of detector array 66. The cathode ofAPD detector element 97 is connected to a programmable detector biasvoltage generator 99 (V_(DET)). The inverting (−) input of differenceamplifier 148 also connects to a feedback circuit 150 which may be aresistor, or may be a transistor configured as a variable resistance, ormay also contain frequency selective elements such as capacitorsconnected in parallel, and/or small inductors connected in series. Thesecond terminal of the feedback circuit connects to the non-invertingoutput of difference amplifier 148. This configuration is often termed atransimpedance amplifier when the feedback circuit 150 is a resistor,and is well suited to API) or PIN diode inputs, which resemble currentsources in some respects. Use of a difference amplifier in this caseprovides a low noise response at low input signal levels, white at thesame time compressing gracefully when subjected to high level inputsignals as is often the case with highly reflective objects (stop signs)positioned in the near field of short range sensor 22. A seconddifference amplifier 152 with a fixed gain is cascaded to provideadditional dynamic range. Typical values for transimpedance gain are inthe range of 50-250 kohms, depending on the pulse widths chosen for theilluminating pulses, and may be programmable in some embodiments.Typical values of voltage gain for second difference amplifier 152 arein the range of 10-50, and again may be programmable in someembodiments. The configuration of second difference amplifier 152 isinverting, with a non inverting (+) input connected to the invertingoutput of first difference amplifier 148. The inverting (−) input ofsecond difference amplifier is connected to the non-inverting output offirst difference amplifier 148. The two cascaded inverting stages give adifferential output having the same sense as the input optical pulsedetected by detector element 97 at non-inverting output V_(LIM)(+). Athird differential stage may be used to extend dynamic range evenfurther in alternative embodiments, and the number of cascaded stagesmay be extended indefinitely with some limitations imposed by the natureof integrated circuits. One major limitation is the difficulty ofisolating input from output, preventing regeneration. A secondlimitation on gain, again imposed by the limited isolation achievable inan integrated circuit process, occurs between neighboring unit cellelectrical circuits. Unit cell gain must therefore be limited to keeplow level signals parasitically coupled from a brightly illuminatedadjacent unit cell, from interfering with the low level input signalfrom individual detector element 97.

FIG. 12 is a detailed electrical schematic of the difference amplifier148 of FIG. 11. The preferred embodiment utilizes an n-channel MOStransistor 154 with the gate as the inverting input. The gate of amatching n-channel MOS transistor 156 is the non-inverting input, andthe source terminal of NMOS transistor 156 is connected to the sourceterminal of NMOS transistor 154, completing the differential pair. Athird NMOS transistor 158 has the drain terminal connected to the commonjunction of NMOS transistor 154 source and NMOS transistor 156 source.The gate of NMOS transistor 158 is connected to programmable voltagebias VB1. The source of NMOS transistor 158 is connected to circuitground, and the transistor behaves in this circuit as a programmablehigh value load resistance, completing the differential amplifier.Connected in like manner as a high value pull-up resistance is p-channelMOS transistor 160, with the drain connected to the drain terminal ofNMOS transistor 154. The gate of PMOS transistor 160 is connected to aprogrammable voltage bias VB2, which sets the value of the variableresistance between the source and drain of PMOS transistor 160. Thesource terminal of PMOS transistor 160 is connected to the positivevoltage supply VDD, and the value of the variable resistance in thechannel of PMOS transistor 160 is set by the difference between VB2 andVDD. PMOS transistor 162 is connected to the drain of NMOS transistor156, and performs in an identical manner as PMOS transistor 160, as avoltage programmable pull-up resistance for NMOS transistor 156 of thedifferential pair. NMOS transistor 164 is configured as a unity gainbuffer amplifier in the familiar source-follower topology. The gate ofNMOS transistor 164 is connected to the drain of NMOS transistor 154,the inverting output of the differential pair. The drain of NMOStransistor 164 is connected to the positive voltage supply VDD, and thesource connected to the drain of NMOS transistor 166 which is againconnected as a high value programmable load resistance, completing theunity gain buffer amplifier circuit. The source terminal of NMOStransistor 166 is connected to circuit ground. The gate of NMOStransistor 166 is connected to a third programmable voltage bias VB3,which sets the resistance in the channel between the source and drain ofNMOS transistor 166. NMOS transistors 168 and 170 are likewise connectedto the non-inverting differential amplifier output as a unity gainvoltage buffer amplifier, operating in like manner to NMOS transistors164 and 166. Feedback impedance in this case is a resistance 150connected between the buffered inverting output, and the gate of theinverting input transistor 154. The feedback impedance may alternativelybe connected directly between the gate and drain of NMOS transistor 154depending on a number of other design considerations.

FIG. 13 is the electrical schematic for a semiconductor laser driversuitable for producing high power and short duration laser pulsessuitable for the pulsed laser transmitter 72 of FIG. 5. It is alsopossible to use the circuit as an analog modulator. A first NMOStransistor 172 is connected so as create a current through laser diode190. The gate of NMOS transistor 172 is driven by a logic signal LS 194which is generated upon command from control processor 74. Logic signalLS is a low power logic signal which may be a single digital pulse, aseries of digital pulses, or an analog modulation waveform. For a logiclevel signal, NMOS transistor turns on fully, and the channel impedancefrom drain to source is at a minimum. The amount of current conductedthrough laser diode 190 depends on the curve of transistor 172, theseries resistance of laser diode 190, the value of limiting resistor186, and the initial bias voltage VBIAS, generated by the programmablevoltage source 180. In the case of a digital modulation sequence, LS isa high enough voltage level which will cause NMOS transistor 172 toconduct with minimum resistance in the channel between source and drainterminals. The cathode of laser diode 190 is connected to the drain ofNMOS transistor 172. The anode of laser diode 190 is connected to alocal storage capacitor 188, and to a fuse 186. The value of localstorage capacitor is chosen to enable a fast rise time through laserdiode 190 at the initial application of the logic signal LS. The valueof global storage capacitor 184 is typically chosen so as to deliver allthe energy needed during a pulse sequence, and the source impedance ofbias generator 180 selected to be able to replenish global storagecapacitor in the time between pulse sequences. Fuse 186 is designed toensure there is no thermal runaway within a failed laser diode 190 whichcould short out the entire array of diodes. This fuse 186 is typicallynot required for VCSEL arrays, due to their inherent resistance tothermal runaway, but is nonetheless included as an additional circuitprotection. Fuse 186 is shown in the schematic as a low valueresistance, as it may be realized on a circuit card or ceramic circuitsubstrate in the form of a printed resistor. Programmable voltage source180 is adjusted by a set of digital inputs 182 from control processor74. The laser diode structure shown within dashed line boundary 192 oflaser diode 190, local storage capacitor 188, and fuse 186 may berepeated as often as needed to yield the required power. Likewise, theNMOS modulating transistors may be wired in parallel, to yield therequired current necessary for the size of the laser diode array. Thecircuit within dashed line boundary 206 is a pre-bias circuit, which maybe eliminated in some purely digital designs, or may alternatively beused as an analog modulator circuit. The primary use of the pre-biascircuit 206 is to eliminate turn-on delays associated with some laserdiodes as they transition from zero bias through a square law regimeassociated with LED operation, and into a more linear region associatedwith the initiation of a lasing mode within the cavity. The pre-biasinput LP 194 may initially be at or near zero, prior to a pre-triggersignal LP being applied. In the case of digital modulation, LP is aswitched logic level, and the amount of pre-bias is set by the voltagedivider between fixed resistor 196 and programmable resistor 200.Programmable resistor 200 is set by digital logic inputs 198 at start-upand may be adjusted or refreshed between laser pulse sequences. Sincethere is initially no current flowing through sense resistor 204, erroramplifier 178 will begin integrating higher at a rate determined by theoutput impedance of error amplifier 178 and the value of capacitor 202.As the output voltage of error amplifier 178 increases, the gate NMOStransistor 174 which is connected to this output will slowly turn NMOStransistor 174 on. As NMOS transistor turns on, current begins flowingthrough current sense resistor 204, which is then buffered through aunity gain stage 176, and the output voltage applied to the invertinginput of error amplifier 178, which completes the feedback loop. Insteady state conditions, the current through sense resistor 204 timesthe value of resistor 204 is controlled by error amplifier 178 to be thesame as the voltage present at the (+) input of error amplifier 178.Alternatively, a time-varying signal may be presented at the pre-biasinput LP 194, and the laser diode array modulated in an analog fashion.The value of capacitor 202 may be adjusted automatically by realizingcapacitor 202 as an array of switched capacitors connected in parallelin the feedback loop of error amplifier 178 (these are not shown). Anumber of additional NMOS transistors 174 may be connected in parallelas well, depending on the size of the laser diode array being driven.

FIG. 14 is a top or plan view of the auxiliary ladar sensor assembly 208which may be mounted to a vehicle 2 embedded within a tail light, brakelight, or turn signal assembly, or alternatively as a dedicatedauxiliary sensor embedded in a door panel, roof column, or bumper zoneof the vehicle 2. A durable molded plastic envelope 210 encloses theassembly, which has features for both retention and connection to theelectrical systems and controls of vehicle 2. In the embodiments of theauxiliary ladar sensor which incorporate signal lights into theassembly, a number of light emitting diode (LED) chips 212 are arrangedin a pattern within the assembly designed to produce the desiredvisibility or illumination in concert with an appropriate diffusing lensor diffractive element 240, shown in this instance as an array ofdiffractive elements in FIG. 15. Each LED has an active area 214 fromwhich light emits upon application of an electric current. A diffusinglens or diffractive array 216 is incorporated into the envelope 210shown here and also in FIG. 15 above a solid state laser 226. A lightcollecting and focusing lens element 218 is shown here incorporated intoa transparent plastic envelope 210. Retention features 220 and 221, hereshown as ramps or snaps, are integrally formed with envelope 210, andare used to secure the auxiliary ladar sensor 208 within a cutout in avehicle 2 body panel. The body panel cutouts are shaped to receive andsecurely retain retention features 220. A section line AA is drawnthrough the assembly and illustrated in FIG. 15 showing greater detailsof the internal workings.

FIG. 15 shows a number of important features of the auxiliary ladarsensor 208 illustrated in FIG. 14. Envelope 210 both encloses thecircuit assembly and may perform as a diffuser in diffusing light fromLED chips 212 and solid state laser 226. A number of diffusingstructures 240 may be embossed, molded, or otherwise formed to aid inthe direction and diffusion of signaling and illuminating lightemanating from LED chips 212. Likewise, a diffusing structure 216 may beembossed, molded, or otherwise formed above solid state laser 226 to aidin directing and diffusing pulsed laser light into the surroundingenvirons. Envelope 210 also has internal wedge shaped bosses 238integrally molded on an interior surface to act as stops for themounting of circuit substrate 222. In this instance, circuit substrate222 is an aluminum nitride thick film ceramic circuit, though a PCboard, plastic molded, steel/porcelain, or other ceramic substrate maybe used in the alternative. LED chips 212 are attached to an uppersurface using solder balls. A solid state laser 226 formed in the shapeof a disc is mounted to an upper surface of circuit substrate 222 usingsolder or heat conductive epoxy. In this case solid state laser 226 is afour layer sandwich with a bottom layer attached to circuit substrate222. The first (bottom) layer is a dielectric mirror in this caseconsisting of alternating layers of optical grade materials havingcontrasting indices of refraction. The mirror must be transmissive atthe pump wavelength of 976 nanometers and reflective at the lasingwavelength of 1540 nm. The second (white) layer is the active gainmedium, in this design erbium doped phosphate glass, though other erbiumdoped glasses, neodymium-YAG, or other suitable crystal may be employed.The third layer is a q-switch material of a saturable absorber whichbleaches at a specified threshold power level. The fourth (top) layer isa mirror surface which may be a dielectric mirror similar to the firstlayer, or may be a metallic reflector. In either case, it should reflectboth the pump light wavelength at 976 nanometers and the lasingwavelength of 1540 nm. A series of circular openings 228 are formed incircuit substrate 222 which allow for the light from the pump laser 224to pass through the substrate. Pump laser 224 in this embodiment is arectangular array of 976 nanometer VCSELs which emit vertically. Thepump laser diode array 224 is attached to circuit substrate 222 bysolder balls which are reflowed during the conventional flip-chipcircuit assembly process. An optional hermetic cover 230 made of Covar®or other suitable metal, plated for solderability, is also soldered orbrazed to the bottom side of circuit substrate 222 to hermetically sealboth the pump laser array 224 and the solid state laser assembly 226from the environment. In the case where solid state laser 226 isattached by solder to circuit substrate 222, a metallization must beplaced on the underside of the chip, typically a titanium/nickel/goldscheme which is applied during successive physical vapor deposition(PVD) coating sequences. Openings in this metallization must be providedfor, typically accomplished by photolithography, to allow pump lightfrom pump laser array 224 to illuminate the active region of solid statelaser 226. Over the top of solid state laser 226 is a hermetic windowcover 232, typically made of Covar® or other suitable metal, plated forsolderability, and soldered or brazed to the top side of circuitsubstrate 222. A transparent window 234, making a hermetic glass tometal seal is assembled to the metal tub which forms the basis of thecover 232, prior to mounting to the circuit substrate 222. Transparentwindow 234 may also be a lens, lens array, or array of diffractiveelements. At the right of FIG. 15, ROIC 64 is mounted to circuitsubstrate 222 by solder or conductive epoxy. A detector array 66 ismounted atop ROIC 64 by indium bumps or solder balls, reflowed by theappropriate process. Wirebonds extend laterally from ROIC 64 and arewedge bonded to pads at the surface of circuit substrate 222. Typically,wirebonds are gold wire and the bonding pads gold over other metalconductor, though other material systems may be used. A second hermeticcover 232 is mounted over the hybrid assembly of ROIC 64 and detectorarray 66 which also has a transparent window glass 234 mounted therein.Transparent window glass 234 may also be a refractive or diffractivefocusing element. Data reduction processor 60 is flip chip soldereddirectly beneath ROIC 64 on an opposing side of circuit substrate 222,making electrical connections through circuit substrate 222. Solderballs 242 are reflowed during the assembly of circuit substrate 222. Astorage capacitor 246 stores enough energy to fire a pulse from solidstate laser 226. A connector 244 receives a mating connector from thefiber cable and wire harness 48 connected to an intermediate ladarsystem controller 24 or directly to the vehicle 2 electrical systems 28in some designs. The connector 244 may have electrical contacts forreceiving electrical power and ground from vehicle 2. Other electricalcontacts in connector 244 may be used for bidirectional transfer ofdata, control, and status signals. Connector 244 may also have opticalmating surfaces for bidirectional transfer of optical data, control, andstatus signals over wiring harness 48. An optional epoxy dome 248 may beapplied over data reduction processor 60 and any other exposedelectrical connections on circuit assembly 222, at any time subsequentto the final soldering operations. Additionally, an epoxy fillet 236 isapplied to secure circuit substrate 222 and the assembly thereon, toenvelope 210. The forming of epoxy fillet 236 may be eliminated in favorof staking, plastic reflowing, or other methods of securing circuitsubstrate 222 to envelope 210. Retention features 220 are shown here ina side vide which illustrates the ramped section of plastic molded beamsprojecting inward which will deflect upon insertion in the mating bodypanel cutout, and then spring back once the thickness of the panel iscleared. The outer surface of the vehicle 2 body panel will then restsecurely against a panel stop 221, which is integrally formed withretention features 220, and effectively sets the depth of insertion ofthe ladar sensor assembly 208.

FIG. 16 is a plan view similar to FIG. 14, with noted exceptions of analternative embodiment of auxiliary ladar sensor assembly 208 employingan electronically modulated VCSEL array 224 as the pulsed lasertransmitter. Improved lower inductance and more reliable flexiblecircuit connections are also used to electrically connect both ROIC 64and detector array 66. In this drawing, the envelope 210 is unmodified,and has been removed to better expose the inner workings of thisalternative embodiment. Circuit substrate 222 is seen supporting anarray of signaling or illuminating LEDs 212. A section line BB is drawnthrough the assembly and illustrated in FIG. 15 showing greater detailsof the internal workings.

FIG. 17 shows a number of features along line BB of the circuit assemblyshown in FIG. 16, and exposes additional details. An array of lenselements 250 are secured in access bores 228 by epoxy, staking, orplastic reflow. The lens elements 250 may be glass, or plastic, and mayhave convex, concave, or planar geometry, and may have flat, circular,or be elliptical surfaces depending on the optical design requirementsof the particular auxiliary ladar sensor installation. Hermetic windowcovers 232 are soldered in place as described above, and may have cleartransparent windows, or may have refractive or diffractive lens elementsformed thereon. Storage capacitor 248 is of a much greater capacity, dueto the requirement for all the energy to be delivered during a fewnanoseconds instead of the hundreds of microseconds in the case of anoptically pumped gain medium as described with respect to FIGS. 14 and15. A new mezzanine level circuit substrate 252 formed in the shape of apicture frame is mounted atop main circuit substrate 222 at the right ofFIG. 17, and serves to make electrical connections to ROW 64 anddetector array 66. Beam leads 254 are formed on a flexible circuitsubstrate of Mylar or Kapton and are connected with solder to ROIC 64.This type of circuitry is often referred to as rigid-flex, combining thefeatures of a rigid PC board 252 with the advantages of flexible circuitconnections 254. The picture frame shape allows the mezzanine PC boardto fit over the rectangular ROIC 64 closely, making the connections asshort as possible, thus lowering inductive bounce from a plurality ofoutput drivers, and lowering the impedance of ground and powerconnections at the higher frequencies characteristic of high performancecircuits. Higher accuracy range estimations typically result fromincreased sampling rates, and therefore the lower parasitic inductancepackaging utilizing the mezzanine picture frame approach should yieldmajor improvements in performance as clock rates and sampling rates moveever higher. The mezzanine PC 252 may be secured to main circuitsubstrate 222 by a thin layer of epoxy and by a number of gold platedberyllium copper pins 253 which are staked through large diameter vias(shown as dashed lines) in mezzanine PC 252 and through mating viasformed in main circuit substrate 222. The vias, represented here as adashed line column, typically connect with an internal ground plane onmain circuit substrate 222, and are soldered both at the top ofmezzanine PC 252, and at the bottom of main circuit substrate 222. Otherconnections between mezzanine PC 252 and main circuit substrate 222 maybe through solder bumps, beam leads, plated through vias, or edgeplating on mezzanine PC 252. The preferred material for mezzanine PC 252is FR-4, but other circuit materials may be used with the same effect.Beam leads 256 connecting to the top of detector array 66 may be assimple as a thin sheet of gold plated beryllium copper, since the topconnection to the detector array is typically only one line, a highvoltage detector bias. In the simple case, beams leads 256 comprisingone or more beryllium copper sheets are attached after mezzanine PC 252is secured and connected, by soldering to the top of mezzanine PC 252,and by conductive epoxy or low temperature solder to a detector biasvoltage grid connection atop detector array 66. In embodiments whichrequire a greater number of connections, beam leads 256 may be anotherflex circuit attached by soldering to the top of mezzanine PC 252, andby conductive epoxy or low temperature solder to a number of metallicpads atop detector array 66.

FIG. 18 is a diagram showing the mating of detector array 66 withreadout IC 64. Row amplifiers 258 and column amplifiers 264 allow theoutput from a unit cell electrical circuit 260 to be output as part of arow output or column output read cycle. All signals to and from readoutIC 64 are communicated through bond pads 266 at the periphery of theROIC 64. FIG. 19 shows details of the placement of the indium bump 262atop each unit cell electrical circuit 260 which is then compressed anddeformed under temperature and pressure as part of the bonding processwhich mates detector array 66 to readout IC 64. The indium bump 262 mayinstead be a low temperature solder bump, which may be reflowed topermanently bond detector array 66 to readout IC 64. The arrow shows thedirection of mating, and the top of detector array 66 shows the gridpattern of an optional micro lens array comprised of tens elements 268which collect and focus light into each of the individual detectorelements of detector array 66 formed on the anterior surface.

Having now described various embodiments of the disclosure in detail asrequired by the patent statutes, those skilled in the art will recognizemodifications and substitutions to the specific embodiments disclosedherein. Such modifications are within the scope and intent of thepresent disclosure as defined in the following claims.

What is claimed is:
 1. A collision avoidance system comprising: a vehicle having at least one ladar sensor mounted thereto, the vehicle having a cutout in a body panel, the cutout having a shape adapted to receive and engage a retention feature on the one ladar sensor, and the vehicle also having a first digital processor connected to a wiring harness, a first connector attached at a terminus of said wiring harness, said first connector adapted to mate with a connector of the one ladar sensor, and the first digital processor receiving three dimensional data from the ladar sensor through the wiring harness, and a control system which controls the path of said vehicle, said first digital processor applying controls through said control system to conduct the vehicle along a preferred path; and the ladar sensor comprising a receiving lens, a laser transmitter, said laser transmitter with a modulated laser light output and a diffusing optic adapted to illuminate a scene in a field of view of said at least one ladar sensor, an automatic range correction circuit having a zero range reference output, a two dimensional array of light sensitive detectors positioned at a focal plane of said receiving tens, each of said light sensitive detectors with an output adapted to produce an electrical response signal from a reflected portion of said modulated laser light output, a readout integrated circuit with a plurality of unit cell electrical circuits, each of the unit cell electrical circuits having an input connected to one of the light sensitive detector outputs, each unit cell electrical circuit having an electrical response signal demodulator and a range measuring circuit connected to an output of said electrical response signal demodulator, said range measuring circuit further connected to the zero range reference output, and a detector bias circuit connected to at least one voltage distribution grid of said array of light sensitive detectors; a second digital processor connected to receive data outputs from the range measuring circuits and adapted to conduct operations on said data outputs, and to provide digital outputs to said first digital processor, and a temperature stabilized frequency reference connected to the second digital processor.
 2. The collision avoidance system of claim 1 wherein said laser transmitter comprises a semiconductor laser formed in a semiconducting gain medium with at least one element selected from the set of indium, gallium, arsenic, phosphorus.
 3. The collision avoidance system of claim 1 wherein said modulated laser light output is modulated with a waveform selected from the set of a single Gaussian puke profile, multiple Gaussian profile pulses, a single flat-topped pulse profile, multiple flat-topped pulses, a puked sinewave, and a chirped sinewave pulse.
 4. The collision avoidance system of claim 1 wherein said laser transmitter comprises an optically pumped solid state laser formed in a gain medium selected from the set of yttrium aluminum garnet, erbium doped glass, neodymium doped yttrium aluminum garnet, and erbium doped yttrium aluminum garnet.
 5. The collision avoidance system of claim 1 wherein said two dimensional array of light sensitive detectors is mounted directly to said readout integrated circuit.
 6. The collision avoidance system of claim 1 wherein said control system controls a vehicle system selected from the set of steering, braking, and suspension.
 7. The collision avoidance system of claim 1 wherein said two dimensional array of light sensitive detectors is formed in a semiconducting film having an element selected from the set of silicon, indium, gallium, arsenic, phosphorus, aluminum, boron, antimony, magnesium, germanium and nitrogen.
 8. The collision avoidance system of claim 1 wherein said ladar sensor is integral with an auxiliary lamp assembly selected from the set of a turn signal, taillight, parking light, and brake light.
 9. The collision avoidance system of claim 1 wherein said electrical response signal demodulator comprises: an input amplifier with an output connected to a trigger circuit; a series of analog sampling gates, each sampling gate with an associated analog memory cell, and each of said sampling gates connected to an output of said input amplifier, a sample clock controlling the timing of each of said sampling gates, a selector for selecting each of said sampling gates in sequence, a counter for counting the number of samples, an output amplifier with an input connected to each of said analog memory cells, an output control for selecting a sequence of said analog memory cell contents to be output through said output amplifier, and wherein an input of an analog to digital converter is connected to said output amplifier, an output of said analog to digital converter is connected to an input of a digital processor and said analog to digital converter produces a sequence of digitized analog samples of said electrical response signal, and said digital processor is programmed to demodulate said electrical response signal by operating on the sequence of digitized analog samples using a digital processing algorithm.
 10. The apparatus of claim 1 wherein said electrical response signal demodulator comprises: an input amplifier with an output connected to a first input of a phase comparator, the phase comparator having a phase reference signal connected to a second input, and an output of the phase comparator connected to the input of an integrator, the integrator having an integrator output with an output voltage indicative of the difference in phase between the first input and the second input of said phase comparator.
 11. The collision avoidance system of claim 1 wherein the vehicle further has at least one two dimensional imaging camera sighted to have a field of view overlapping the field of view of the ladar sensor assembly, and the vehicle further having a digital processor adapted to merge data from the ladar sensor with data from said two dimensional imaging camera.
 12. A ladar sensor and vehicle comprising: a vehicle having a cutout in a body panel, said cutout having a shape adapted to receive a mating retention feature, said vehicle further having a first digital processor, a wiring harness and a first connector attached at a terminus of said wiring harness, a ladar sensor comprising; a second connector adapted to mate with the first connector of said wiring harness, receiving optics, a laser transmitter with a modulated laser light output and a diffusing optic adapted to illuminate a scene in a field of view of said ladar sensor, an automatic range correction circuit having a zero range reference output, a two dimensional array of light sensitive detectors positioned at a focal plane of said receiving optics, each of the light sensitive detectors with an output producing an electrical response signal from a reflected portion of the modulated laser light output, a readout integrated circuit with a plurality of unit cell electrical circuits, each of said unit cell electrical circuits having an input connected to one of the light sensitive detector outputs, each unit cell electrical circuit having an electrical response signal demodulator and a range measuring circuit connected to an output of said electrical response signal demodulator, said range measuring circuit further connected to the zero range reference output, a detector bias circuit connected to at least one voltage distribution grid of the array of light sensitive detectors, a second digital processor connected to receive outputs from the range measuring circuits, and a temperature stabilized frequency reference connected to the second digital processor; and, an envelope enclosing the ladar sensor, said envelope having at least one transparent section, and said envelope also having the mating retention feature and mounted to the vehicle.
 13. The ladar sensor and vehicle of claim 12 wherein said wiring harness has at least one optical waveguide.
 14. The ladar sensor and vehicle of claim 12 wherein said first connector has electrical contacts.
 15. The ladar sensor and vehicle of claim 12 wherein said first connector has at least one optical mating surface.
 16. The ladar sensor assembly and vehicle of claim 12 wherein said envelope is molded from a transparent plastic.
 17. The ladar sensor and vehicle of claim 12 wherein said retention features are comprised of beams with tapered ramps which deflect upon engagement with a body panel cutout of a vehicle and spring back towards a rest position, thereby retaining the ladar sensor within the cutout when fully inserted into said panel.
 18. The ladar sensor and vehicle of claim 12 wherein said laser transmitter comprises a vertical cavity surface emitting laser formed in a semiconducting gain medium with at least one element selected from the set of indium, gallium, arsenic, phosphorus.
 19. The ladar sensor and vehicle of claim 12 wherein said modulated laser light output is modulated with a waveform selected from the set of a single Gaussian pulse profile, multiple Gaussian profile pulses, a single flat-topped pulse profile, multiple flat-topped pulses, a pulsed sinewave, and a chirped sinewave pulse.
 20. The ladar sensor and vehicle of claim 12 wherein the laser transmitter comprises an optically pumped solid state laser formed in a gain medium selected from the set of yttrium aluminum garnet, erbium doped glass, neodymium doped yttrium aluminum garnet, and erbium doped yttrium aluminum garnet.
 21. The ladar sensor and vehicle of claim 12 wherein the two dimensional array of light sensitive detectors is mounted directly to said readout integrated circuit.
 22. The ladar sensor and vehicle of claim 12 wherein said ladar sensor comprises a plurality of electrical components mounted to at least one circuit substrate within said envelope.
 23. The ladar sensor and vehicle of claim 12 wherein said ladar sensor is integrated into an auxiliary lamp assembly selected from the set of a turn signal, taillight, parking light, mirror assembly, and brake light.
 24. The ladar sensor and vehicle of claim 12 wherein said vehicle further has at least one two dimensional imaging camera sighted to have a field of view overlapping said field of view of said ladar sensor, and said vehicle further having a digital processor adapted to merge the data from said ladar sensor with data from the two dimensional imaging camera.
 25. The ladar sensor and vehicle of claim 12 wherein the laser transmitter is enclosed by a hermetic cover.
 26. The ladar sensor and vehicle of claim 12 wherein said two dimensional array of light sensitive detectors is enclosed by a hermetic cover.
 27. The ladar sensor and vehicle of claim 12 wherein said laser transmitter is an array of semiconductor lasers modulated by a current controlled by at least one transistor. 